1. Field of the Invention
The present invention relates to a control apparatus of a generator for vehicle driven by rotation of an engine and to a control method of the generator.
2. Description of the Related Art
A vehicle such as automobile is generally provided with a generator driven by rotation force of a crankshaft of an engine in order to charge a battery acting as a power source with an electric power. In the case of decrease in battery voltage detected at a voltage detection terminal by a regulator or increase in capacity of an electric load, the generator increases a generated current by making larger a duty ratio of an exciting current inputted to a field coil. On the other hand, in the case of decrease in capacity of the electric load, the generator decreases a generated current by making smaller the duty ratio of the exciting current. Further, upper limit of the duty of the generated current can be set by a control signal inputted from outside. As for the limitation of duty of the exciting current, another method has been proposed. In this another method, a generator itself has a function of limiting the duty of the exciting current to be smaller than a predetermined value at cooling time as disclosed in the Japanese Patent Publication (examined) No.38720/1994 (pages 3-4, FIGS. 1 and 2).
It is a recent trend that various electrical components have been mounted on a vehicle and power consumption has been increased. Under such a background, a high power type generator with high generating performance has been increasingly adopted. In this respect, an output of the generator at cooling time is generally larger than that at heating time which is a nominal output, and drive torque is also larger than that at heating time. The drive torque becomes the largest near the number of revolution when the engine is idling. As a result, in the range of starting a high power type generator mounted on a vehicle at cooling time as well as idling operation, there is a possibility that load on the engine comes to be large, engine speed is reduced, and timing belt is abraded.
As means for suppressing the drive torque of the generator at cooling time, it may be an idea that a generator itself has a function of suppressing a torque, as described above. However, in such a construction, a problem exists in that any additional circuit is required for achieving the suppression in torque, eventually resulting in increase in cost of the generator itself.